Quercus wutaishanica shrub affects temperate forest community composition and soil properties under different restoration stage

Quercus wutaishanica is the dominant tree species in the natural ecosystem restoration of temperate forests in China, and it plays an active role in maintaining ecological balance. However, little is known about how ecosystem versatility develops during the restoration of forest ecosystems dominated by Q. wutaishanica. In this study, we investigated the species composition of the Q. wutaishanica community, soil nutrients, and their functional traits at various restoration stages, and comprehensively analyzed the correlations among them. At the early stage of restoration (10 years of restoration), there were Spiraea pubescens and Syringa pubescens in Q. wutaishanica community (87% of the total species), while had a larger niche width. In the middle of restoration (30 years of restoration), shannon and evenness indices were the largest, while soil total carbon, ammonium nitrogen and chlorophyll content of Q. wutaishanica leaves were the highest; among them, soil total carbon was 15.7% higher than that in 10 years of restoration, 32.4% higher than that in 40 years of restoration, ammonium nitrogen was 71.7% higher than that in 40 years of restoration, and chlorophyll content was 217.9% higher than that in 10 years of restoration, and 51.8% higher than that in 40 years of restoration. At the later stage of restoration (40 years of restoration), Lonicera ferdinandii occupied the dominant ecological niche, and soil available nitrogen, available phosphorus content and leaf thickness were the largest; while AN was 10.9% higher than that of 10 years of restoration, 16.5% higher than that of 30 years of restoration, AP was 60.6% higher than that of 10 years of restoration, 21.6% higher than that of 30 years of restoration, leaf thickness was 22.3% higher than that of 10 years of restoration, 84.9% higher than that of 30 years of restoration. However, the restriction of various soil nutrients was reduced. Our study highlighted the effectiveness of soil resource availability in plant communities during restoration, reduced competition for light among plants, and altered species richness. Furthermore, changes in the interrelationship between plant community composition and leaf functional traits of the dominant species responded positively to community restoration. These results further deepen our understanding of forest management and restoration of forest communities. In the future, it is necessary to comprehensively consider the influence of various factors on forest community restoration.


Introduction
The Grain to Green Program (GTGP), Natural Forest Protection Program (NFPP), and Three-North Shelterbelt Program (TNSP) are a series of important plans for the restoration of natural ecosystems in China, which significantly impacts the maintenance of ecosystem functions, biological diversity, and carbon balance [1][2][3].With the implementation of ecological restoration plans, most evergreen broad-leaved forests are currently at different restoration stages after being restored to secondary forests [4,5].Quercus wutaishanica is the dominant tree species in warm and temperate deciduous broad-leaved forests and mixed broadleaf-conifer forests in China and plays a positive role in soil and water conservation and ecological balance maintenance [6].Therefore, improving our understanding of the changes in plant diversity, soil properties, and plant functional traits during ecosystem restoration is essential for coping with abiotic and biotic stresses (climate change, insect pests, drought, etc.) and for the proper management of forests.
During forest ecosystem restoration, plant diversity has been studied as an indicator of community species composition and diversity [7].Long-lived tree species can reduce the fragmentation of the forest landscape at the spatiotemporal scale [8], and tree species with larger canopy gaps are conducive to the replenishment of early stages [9].With restoration, the number of dominant species and pioneer species has increased [10,11].Therefore, the study of plant diversity at various stages of restoration can provide a theoretical basis for the restoration and reconstruction of forest ecosystems.However, unlike the traditional use of plant diversity in assessing the restoration stage of forest ecosystems, various aspects of nutrient accumulation in forest ecosystems have been developed in recent studies [12,13].An increase in forest carbon sink can improve the diversity and stability of plant community structure [14,15], while nutrient inputs (e.g., nitrogen or phosphorus) have significant negative effects on plant community richness, thus increasing plant community similarity and decreasing species diversity [16].
An increasing number of studies have shown that in addition to disturbances, environmental conditions (soil properties) also one of the factors affect species diversity during the restoration stage [17].Soil nutrients, as important regulators of vegetation regeneration, exhibit different characteristics at different forest restoration stages, and are closely related to forest restoration speed [18].The establishment of woody plants is delayed by the coverage of annual plants when nutrients are abundant [19].With the depletion of soil nutrient resources, plants with slow growth rates have more advantages than those with fast growth and high reproductive rates [20].In addition, the accumulation of soil nutrients depends on the vegetation composition.During the restoration stages, soil total phosphorus content decreased gradually, whereas total nitrogen content and alkali-hydrolyzable nitrogen in organic matter increased significantly [21].Other studies have indicated that soil carbon, nitrogen, and phosphorus contents first decreased and then increased with restoration, and were higher during the late restoration periods [22].More studies have suggested that with an increase in tree biomass, soil nutrients, organic matter, and carbon storage also increase [1].In conclusion, the differences between the dominant species and the number of species in the forest restoration stage are closely related to soil nutrients [23].Soil nutrients, including exchangeable cations, total nitrogen, and phosphorus, have strong geographical heterogeneity and affect the composition of plant species at different restoration stages as well as species functional traits [24].

PLOS ONE
In recent years, studies on plant functional traits have greatly improved our understanding of plant functions and characteristics during forest restoration [25,26].Previous studies have shown that the ecological strategies of plants switch between resource acquisition and conservation during the restoration stage [27].However, plants must make trade-offs between leaf physiological traits and nutrient storage to better adapt to biotic and abiotic factors during restoration [28].From dry to wet conditions, plants use more water to maintain their growth while decreasing photosynthesis to increase protein consumption in leaves with lower nitrogen content [29].At the early stage of restoration, herbaceous plants dominate, and woody plants improve their photosynthetic capacity by accumulating nitrogen in leaves to maintain dominant growth [30].Overall, biomass allocation among plant organs is driven by environmental conditions, but functional traits may also be potential variables for biomass allocation [31].
Previous studies have suggested that the dominant geographical boundary factors (climate and disturbance intensity) affect the distribution of Q. wutaishanica in China [32], which focused on the relationship between spatial distribution patterns, plant functional traits, nutrients, soil carbon, nitrogen, and phosphorus in Q. wutaishanica communities in the Taiyue and Ziwuling Mountains [33][34][35][36].Therefore, we proposed the following hypotheses: (1) there would be differences in species diversity and richness within communities at different restoration stages of Q. wutaishanica communities; (2) changes in species composition during the restoration stage of Q. wutaishanica communities may also have an effect on soil characteristics; and (3) changes in leaf functional traits of dominant plants in Q. wutaishanica communities would respond differently to the restoration stage.

Study site
This study was conducted in the National Nature Reserve of the Liupanshan Mountains (351 5 0 to 35˚41 0 N and 106˚09 0 to 106˚30 0 E), which is located in the south of the Liupanshan Mountains in Guyuan City (Longde and Jingyuan counties) of the Ningxia Autonomous Region, with a total area of 67,800 ha, and is one of the largest forest areas in northwest China (  The National Nature Reserve of the Liupanshan Mountains is located at the edge of the northern agriculture/pastoral ecotone and a semi-humid to semi-arid transitional zone in North China.Cold and dry air flows were interlaced.It is hot and rainy in the summer and dry and cold in the winter.The mean annual temperature is 5.8˚C, the coldest month (January) is −7˚C, and the hottest month (July) is 17.4˚C.The mean annual precipitation is 676 mm, and the mean annual evaporation is approximately 1426 mm.The frost-free period was approximately 120 days, and the annual total sunshine duration was 2100-2400 h.There are more than 80 rivers in the Liupanshan Mountains, all of which belong to the Yellow River System.The soils in the area are grayish brown.
Through visits to the Forest Tree Breeding Center, Liupanshan Forestry Bureau, Guyuan, and combined with information detailed by local villagers, we selected areas that were completely destroyed before restoration, where the shrubs were cut down and the dominant tree species were restored naturally.In July 2019, we identified three shady slope sample stands that gradually extended from east to west, from near the Yejia village in Baimian Town to Liupanshan National Nature Reserve.The first sample stand was Xilianggou (E106˚21 0 , N35˚23 0 ), which was restored late and only gradually with the recent reduction of human activities such as logging and grazing, and the restoration time is about 10 years from now (10 y).And the elevation was about 1849.13 m.The second sample stand was Dawan (E106˚21 0 , N35˚23 0 ), which was fenced and restored in the 1990s, and the restoration time was about 30 years from now (30 y).The elevation was about 1882.13 m.The third sample stand was Dadaogou (E106˚21 0 , N35˚23 0 ), located in the Liupanshan Nature Reserve, which was fenced and restored in the late 1970s, about 40 years ago (40 y).And the elevation was about 1912.98 m (Table 1).
The main vegetation types in the Liupanshan Mountains are temperate coniferous forests, evergreen Bambusoideae shrubs, secondary deciduous broad-leaved forests, deciduous broadleaved shrubs, and grasslands.The temperate coniferous forest is dominated by Pinus armandii, the evergreen bambusoideae shrub by Fargesia nitida, and the secondary deciduous broadleaved forest by Q. wutaishanica, Betula platyphylla, Betula albosinensis and Populus davidiana [37].

Community investigation and species composition index calculation at various restoration stages
We investigated the composition of plant communities in three sample stands and determined soil physicochemical properties and plant functional traits.Four transect lines with the same slope direction were set in each stand, and the spacing of each line was greater than 20 m.A 10 ×10 m quadrate was randomly set on each line transect using a simple random method.Each sample stand has 4 quadrats, for a total of 12 quadrats.All woody plants with a base diameter �1 cm in each quadrate were counted, and their species names, plant height, plant number, and coverage were recorded.The plant species were identified with the method of Cheng et al. (2020) and combined with data from http://ppbc.iplant.cn/[38].
Species diversity indices, including shannon index [39], evenness index, and richness index [40,41], were calculated according to the following equations: where P i = n i /N, n i represents the number of individuals of a species, N is the total number of species, and S is the number of species.Niche width was calculated using the shannon formula [42] and niche overlap was calculated using the Pianka index [43] (Fig 3).shannon index: (4) Pianka index: (5) In the formula, B i is the niche width of i species; P ij = n ij / N i , n ij represents the importance value of i species in j resources, N i is the sum of the importance values of i species in total resources, P ij is the proportion of the importance value of i species in j resources to that species in total resources, r the number of quadrats, and O ik is the overlap index of species i and k.

Analysis of soil nutrients at various restoration stages
Soil samples were collected from three sample stands at various restoration stages with consistent environmental and terrain conditions.In each 10 × 10 quadrate, nine sampling points were selected according to the S-shape sampling method, and the soil from each of the three sampling points was mixed into one soil sample, while soil mixtures with a depth of 0-10 cm were collected with a shovel.Twelve soil samples were collected at three different restoration stages, and the collected soil samples were placed in valve bags and brought back to the laboratory.Each soil sample was divided into two parts.One part was screened a 0.25 mm sieve and then dried naturally.After grinding, the total organic carbon (TC, g/kg), total nitrogen (TN, g/ kg), total phosphorus (TP, g/kg), available phosphorus (AP, mg/kg), and available potassium (AK, mg/kg) content were measured [44].Another portion of fresh soil from each sample was screened using a 2 mm sieve and stored at 4˚C for the measurements of soil ammonium nitrogen (NH 4 + -N, mg/kg), nitrate nitrogen (NO 3 -N, mg/kg), and available nitrogen (AN, mg/kg) contents [45].

Analysis of plant functional traits of Q. wutaishanica
We collected the upper canopy and sunny, pest-free, and fully unfolded leaves of Q. wutaishanica plants from each stand in September 2019.All leaves were placed between two pieces of wet filter paper, placed in a valve bag, and brought to the laboratory for measurement [46].The leaves were divided into two parts on average.One part was used to measure plant functional traits: leaf length-width ratio (LWR), leaf thickness (LT, mm), leaf dry matter content (LDMC, g), specific leaf area (SLA, cm 2 /g), and leaf chlorophyll content (LCC, mg/g).Leaf length was measured as the distance from the petiole-blade junction to the blade tip, and leaf width was measured at the widest part of the blade.A digimatic micrometer was used to measure three positions (front, middle, and back) of the blade close to the main veins, and LT was the average value obtained from the three measurements.Furthermore, leaves were soaked in a petri dish filled with water under 5˚C dark conditions for 12 h, the water on the surface was quickly wiped off with filter paper, and the saturated fresh weight of the leaves was weighed immediately.The leaves were then dried in an oven at 75˚C to a constant weight and their dry weights were measured.LDMC was calculated as leaf dry weight divided by leaf saturated fresh weight.The leaf area was measured using a por.leaf area meter (LI-COR 3000C Area Meter, LI-COR, Lincoln, USA), and SLA was calculated as leaf area divided by leaf dry weight [47].Chlorophyll in fresh leaves was extracted using acetone, and the chlorophyll content was measured using spectrophotometry [48].The remaining leaf samples were placed in an oven at 80˚C for 30 min and then at 60˚C for 72 h.After complete drying, the samples were crushed and sieved through a 0.25 mm.These leaf samples were used to measure the total carbon (LTC, g/kg), total nitrogen (LTN, g/kg), and total phosphorus (LTP, g/kg), according to previous studies [44].

Statistical analysis
Soil nutrients and plant functional traits were analyzed by one-way analysis of variance (ANOVA) using SPSS (25.0), and multiple comparisons were performed for all data using the least significant difference method (LSD).All data are presented as mean ± SE (n = 12).The "Vegan" package was used in R software for non-metric multidimensional scaling (NMDS) analysis [49]."Spaa" package in R software (Version 4.1.0)was used to calculate niche overlap based on levins method, and the corrplot package was used for visualization.The functional richness index (FRic), functional evenness index (FEve), functional divergence index (FDiv), functional dispersion index (FDis) were calculated by "FD" package.The correlations between soil physicochemical properties and plant functional traits and between plant functional traits were calculated using the "psych" package.Redundancy analysis (RDA) was used to establish relationships among species composition, soil physicochemical properties, and plant functional traits at various restoration stages [50].

Species composition of Q. wutaishanica community among various restoration stages
By surveying all species in three different restoration stages, we found 10 species of arbors, 31 species of shrubs, and the most herbaceous species with 42.Among the three different restoration stages, 30 years of restoration contained the most trees with nine species, 10 years of restoration was the second with eight species, and 40 years of restoration had the fewest tree species with four.The number of shrubs after 10 years of restoration was the largest, with 27 species, accounting for 87% of the total; 30 years of restoration was the next most abundant with 16 species, accounting for 51% of the total; and 40 years of restoration was the least abundant with 15 species, accounting for 48% of the total (Fig 2A ).
At the three restoration stages, shannon and evenness indices were the largest at 30 years of restoration, which were significantly different from those at 40 years of restoration (p < 0.05).The richness index was the largest at 10 years of restoration and significantly higher than that at 40

Characteristics of soil nutrients at various restoration stages
The soil TC content was highest at 30 years of restoration and significantly higher than that at 40 years of restoration (p < 0.05).The NH 4 + -N content after 30 years of restoration was higher than that after 40 years of restoration.However, the AN and AP contents in soil after 40 years of restoration were significantly higher than those after 10 and 30 years of restoration (p < 0.05) (Fig 4A).Furthermore, the correlation analysis between the community structure characteristic index and physicochemical properties showed that the richness index of the plant community was significantly negatively correlated with AN, while shannon was positively correlated with TC, but negatively correlated with AN.In addition, FDis and RaoQ scores were negatively correlated with AP (p < 0.05) (Fig 4B).

Plant functional traits of Q. wutaishanica at various restoration stages
Our study indicated that the LTC content of Q. wutaishanica leaves showed little difference between the three restoration stages.LTN content after 30 and 40 years of restoration was higher than that after 10 years, and LTP content decreased with restoration time.The LT index was the highest at 40 years of restoration and was lower at 30 years; LCC was the highest at 30 years of restoration and significantly higher than that at 10 and 40 years of restoration (p < 0.05) (Fig 5A).RDA showed that leaf functional traits and soil physicochemical properties had strong directivity to restoration years, while RDA1 and RDA2 explained 50.9% and 21.37% of the variables, respectively.Among them, LWR, LN:P, LTC, and LC:P were correlated with AP, AN, and NO 3 -N after 30 years of restoration, whereas LTP, SLA, LCC, and LTN were significantly correlated with soil TC, TP, and AK after 40 years of restoration (Fig 5B).

Relationship between community diversity index and plant functional traits of Q. wutaishanica community
Further analysis showed that LTC and LC:P had a negative effect on FDis and RaoQ after 10 years of restoration, while LCC had a positive correlation with evenness (p < 0.05).With the

At the later restoration stages, the composition of the species community changes
Q. wutaishanica plays an important role in forest restoration in the Loess region of northern China [51].Our study highlighted that the species diversity dominated by Q. wutaishanica communities changed with prolonged restoration time, which was consistent with the findings of Craven et al. [52].In general, small-seeded species predominate in the early restoration of young (4-12 years) and middle (16-20 years) forests.However, in old-growth forests, there are some plants related to late restoration (such as large-seeded species and trees) [53].After 10 of restoration, the Q. wutaishanica community had more total species, which was similar to the result that plant species accumulated rapidly during the initial stage of restoration (Fig 2).Although environmental factors (sunlight, evaporation, and soil nutrients) have a significant impact on the distribution of plant species [54], ephemeral plants often dominate the community in the early restoration stage [55].Abbas et al. also found that in the restoration of tropical forest plant communities, the accumulation of plant species mainly occurs in the early stage of restoration (15-20 years) [56].With restoration, the number of shrubs in the middle of the restoration stage (30 y of restoration) decreased.This is similar to previous results showing that with the prolonging of the restoration period, the competition among species in the community intensified, leading to the decline of species [57,58].It is more likely that the community vegetation was dominated by sunny species in the early stage of restoration, and the species composition was differentiated in the middle stage due to random environmental filtering and dispersal restrictions of species colonization and recruitment [56].Especially in forest community restoration, pioneer species dominate the secondary forest community structure [59].An important question in forest restoration is whether the diversity of plant species has improved [58].The species diversity of the Q. wutaishanica community increased significantly after 30 years of restoration compared to that after 10 years of restoration.It is well known that the species richness of immature secondary forests is higher than that of young secondary forest [60,61].Species heterogeneity and diversity changed, probably because of the stronger response of new community species to soil nutrients and environmental changes at the early stages of restoration, as well as the limitation of seed dispersal [57,62].Lasky et al. found that species diversity in tropical forests decreased with increasing restoration period (from 10 to 40 years) [63].Similarly, it was found that after a long period of forest restoration (50 years), species diversity decreased significantly [64,65].Our study found that the species diversity of the Q. wutaishanica community decreased after 40 years of restoration compared to that after 30 years of restoration.This may be because of the existence of pioneer species in the early restoration of the Q. wutaishanica community, which recruited a large number of species, and the lack of abiotic or biotic filtration, resulting in an increase in species diversity.With restoration, the species colonization rate was higher and the mortality rate was lower in the understory, while some dominant species and herbs eventually dominated in the understory, thus changing species diversity [66].In the present study, plant species diversity first increased and then decreased (Fig 2).This unimodal curve was probably due to communities constructed by random dispersal and species colonization during early restoration.In view of the closer relationship between species, the environment was suitable for their expansion, which maximized species diversity in the middle stage of restoration.However, at the later stages of restoration, related species were gradually eliminated due to environmental filtration, which reduced the species diversity in the community [56,67].
Our observations indicated that the plant species richness of the Q. wutaishanica community decreased gradually from 10 to 40 years after restoration (Fig 2B).Studies have shown that species richness gradually stabilizes with community restoration.The former was gradually shaded by the crown canopy, whereas the latter gradually occupied the crown canopy with restoration [61], thus playing the role of filtering restrictions and reducing species richness [68].In addition, a higher soil resource supply and light availability at the initial restoration stage of the plant community increased plant richness.However, as plant community restoration proceeds, the availability of soil resources decreases, reducing consumer competition for light and altering species richness [69].Furthermore, competition among plant consumers, which increases intraspecific community height, also decreases interspecific SLA [69,70].Plant community responses to restoration drivers depend on the underlying characteristics of resident species that influence community diversity during restoration [69].
In the restoration of plant communities, the larger the niche width of the species, the higher the resource utilization efficiency of the species, and the stronger the adaptive capacity to the environment [71].Our results indicated that the niche width of Q. wutaishanica was the largest among the three restoration stages, indicating that Q. wutaishanica was dominant in each stage.The niche width of community restoration dominated by Q. wutaishanica was controlled by environmental selection and random processes; however, random processes may play a large role in the early stage of restoration, while environmental selection plays a dominant role in the middle and late stage [67,72].In addition, niche overlap reflects the similarity in resource utilization among populations.We found that species niche overlap significantly decreased after 40 years of restoration, which was similar to the results of previous studies that symbiotic relationships among plants gradually weakened over time, and competition among species decreased during community restoration at a regional scale [71,72].

At the later restoration stages, the limitation of soil nutrients decreased
Forest ecosystem restoration is determined by the soil environment, especially soil nutrient availability.However, plant growth rate and biomass accumulation respond rapidly to soil nutrients [73].It is believed that species in the early stage of restoration compete with other species by increasing the utilization efficiency of light resources through nutrient accumulation [74].The reason why TC and NH 4 + -N in our study were the largest after 30 years of restoration was also confirmed, while the competitive growth of species increased the utilization of NH 4 + -N by plants and carbon input in soil (such as litter) [75].With the restoration of the Q. wutaishanica community, the dominant species had a niche advantage and the demand for AN content further increased (Fig 4).The competing species died successively, which changed the carbon input to the soil [76].This may explain the strong correlation between TC and community diversity observed in this study.
The change in soil AN content was opposite to that of TC and TP contents in this study and was the lowest after 30 years of restoration.On one hand, species diversity increased the AN utilization by plants, resulting in nitrogen limitation of soil nutrients [77,78]; on the other hand, leguminous plants (Medicago lupulina and Lespedeza bicolor) appeared in 10 and 40-year restoration communities, which increased the fixation of available nitrogen in soil [79].Another study pointed out that soil ammonium and nitrate nitrogen play key roles in community β-diversity composition [80].In our study, the carbon nitrogen ratio and NH 4 + were higher in the community after 30 years of restoration than those after 40 years of restoration, indicating that the ability of soil nutrient mineralization and decomposition gradually decreased during community restoration, and similar results were recorded by Bauhus and Pare [81].

Species composition and leaf functional traits of Q. wutaishanica communities differ in different restoration stages
Plant functional traits are indicators of plant resource utilization strategies and are closely related to various restoration stages of the community.The analysis of plant functional traits can deepen our understanding of community restoration processes and community structure [82][83][84][85].It was observed that the strategy of resource utilization in plants was changed from acquisitive type to conservative type during restoration [86].Here, we found that the SLA and LCC indices initially increased and then decreased with restoration.In plant restoration, owing to differences in soil nutrient allocation, the strategy was changed to a conservative strategy, which was consistent with the findings of Pinho et al. [73].The SLA index increased with the accrue of crown canopy and nutrient utilization, and the SLA index of dominant species decreased with the complexity of the community structure during restoration [87].Our research also confirmed that the SLA of Q. wutaishanica showed similar changes in community diversity and soil NH 4 + -N.Moreover, SLA is affected by both LT and LDMC indices [88].In our study, the LT and LDMC indices decreased at the beginning and then increased with restoration time, and the change in LT was greater.As the LT index was positively correlated with the utilization efficiency of light resources [89], Q. wutaishanica gradually occupied the canopy position as the dominant species in community restoration, which improved the utilization efficiency of light resources by the leaves [90].
The changes in plant functional traits of the dominant species are driven by carbon and other nutrient cycles [91].The higher the leaf nitrogen and phosphorus contents, the greater the photosynthetic rate, while the growth rate and resource competitiveness increased accordingly [92].We found that leaf TN content gradually increased and tended to be stable with the prolonging of the restoration period, which further supports the conclusion that TN content increases with increasing stand age [93].The leaf TP content decreased gradually with restoration, which was caused by various nutrient utilization strategies of different plant types and explained the functional redundancy of soil AP at different restoration stages [94].
Plant-soil interactions are an important determinant of vegetation restoration [95,96].We found a strong correlation between soil TC, FDis, and RaoQ after 10 years of restoration, and the limiting effect gradually decreased, indicating that the resource utilization strategy of Q. wutaishanica changed during community restoration.It has been reported that the reduction in the utilization efficiency of light resources by plants leads to the weakening of the nutrient cycle restriction [73].They also showed that stand age is an important driver of soil carbon input [28].At the early stage of restoration, plants have a strong demand for nutrients, but less input of leaf litter makes it difficult to achieve effective carbon sequestration [91].On the other hand, with community restoration, soil carbon input increased, which increased soil functional redundancy and improved geobiochemical circulation [97].In addition, the effect of higher species richness in the initial restoration stages of plant communities on plant seed quality was also influenced by the supply of soil resources.As restoration proceeds, competition among plant consumers increases intraspecific community height and decreases interspecific SLA [69,70].Our study further confirmed that plant leaf nitrogen content had an important effect on species richness from the late stage of community restoration, which was consistent with previous findings that also reported that changes in plant functional traits affected species richness [98].

Conclusion
Q. wutaishanica is the dominant tree species in natural ecosystem restoration of temperate forests in China, which plays an active role in maintaining ecological balance.However, little is known about how ecosystem versatility develops during the restoration of forest ecosystems dominated by Q. wutaishanica.In this study, we investigated the species composition of the Q. wutaishanica community, soil nutrients, and their functional traits at various restoration stages, and comprehensively analyzed the correlations among them.At the early stage of restoration (10 years of restoration), there were more shrubs in Q. wutaishanica community, while had a larger niche width.In the middle of restoration (30 years of restoration), shannon and richness indexes were the largest, while soil total carbon, total phosphorus, ammonium nitrogen and leaf shape index, chlorophyll content of Q. wutaishanica leaves were the highest.Moreover, the correlation between leaf and soil nutrients was the strongest.At the later stage of restoration (40 years of restoration), soil available nitrogen, available phosphorus content and leaf thickness were the largest.However, the restriction of various soil nutrients was reduced.Our study highlighted the effectiveness of soil resource availability in plant communities during restoration, reduced competition for light among plants, and altered species richness.Furthermore, changes in the interrelationship between plant community composition and leaf functional traits of the dominant species responded positively to community restoration.These results further deepen our understanding of forest management and restoration of forest communities.In the future, it is necessary to comprehensively consider the influence of various factors on forest community restoration.